24 “Now I rejoice in my sufferings for your sake, and in my flesh I am supplementing what is lacking in Christ’s afflictions in behalf of His body, which is the church. 25 I was made a minister of this church according to the commission from God granted to me for your benefit, so that I might fully carry out the preaching of the word of God, 26 that is, the mystery which had been hidden from the past ages and generations, but now has been revealed to His saints, 27 to whom God willed to make known what the wealth of the glory of this mystery among the Gentiles is, the mystery that is Christ in you, the hope of glory. 28 We proclaim Him, admonishing every person and teaching every person with all wisdom, so that we may present every person complete in Christ. 29 For this purpose I also labor, striving according to His power which works mightily within me.”
Supplementing what is lacking: This does not mean that Christ is somehow dying for sin. He is simply recognizing that as a follower of Jesus, He shares in Christ’s afflictions. As Christ was persecuted, so was Paul.
Mystery that is Christ in you: Paul is not speaking of an ambiguous will. He is speaking of Christ in believers. Specifically, Paul likely has in mind Gentiles of whom he was a minister. This was God’s plan of election from the foundations of creation: God always wanted Christ to indwell not only Jews, but Gentiles also. Salvation is not merely forgiveness, but union with Christ, the image of the indivisible God, Himself.
I also labor: Grace never encourages laziness. In fact, God’s grace was Paul’s fuel for labor. But this labor is not apart from Christ. This is not all of Christ and none of Paul. This is Paul’s union with Christ expressed daily. Paul’s desire was to labor, with Christ, to the end that all people would be made complete by grace through faith in Christ. Religion says that we need more of Jesus. But Jesus says that if we believe in Him, we will have everything we need for life and godliness (2 Peter 1:3-4).